نشریه سازه و فولاد
سال سیزدهم شماره 26 (پاییز و زمستان 1398)

A beam-to-column connection has a significant role in the behavior of steel structure under the effect of verity loads. Rigid connection in steel moment frame has a special role in the behavior of these structures. Moreover, the fire resistance of these connections can be important. Among these parameters, steel material used in the connection is important and its investigation seems necessary. In this article, the behavior of 9 steel moment end-plate connections under the effect of various degrees of temperatures was studied using finite element methods through ABAQUS software. The connections have been designed, modeled and analyzed using three types of steel materials. The models verified by the use of an experimental model through elastic and plastic amplitudes up to collapse and during numerical results, the effect of large deformation in the nonlinear region has also been considered. The results of this study show that using of the stiffeners improves connection capacity and performance. The results of this study show that declined slope of moment capacity of connection with stiffener coming in all temperatures and is almost smooth and constant. However, it observed that the declined slope of moment capacity of connection with and without stiffener which designed with low strength steel was less than other connections during 800 to 900 degree which shows better performance of this connection.

The increasing risks resulted by blast loads in current broad and thin plates necessitate the studies and evaluation of these challenges. Practical and cost-effective solutions such as plates enforcement with stiffener are suggested due to high displacement of structure as a result of applied loads. Moreover, application issues and the possibility of developing opening in plates and thus their change of behavior are considered important issues, for which solutions are suggested in this study. Functionally graded plates (FGM) with a power distribution in the direction of thickness are suggested as a solution to this challenge. Accordingly, the present study assesses parameters related to plates with opening including kind, percentage and the position of opening, the mass amount of explosive material, and the parameters related to plates with stiffener including type, count, arrangement of stiffeners, boundary condition and also the joint effect of stiffener and opening using Abaqus Software. The results indicate that opening decreases the plate hardness which consequently increases the amount of displacement. Plate displacement constantly reduces as a result of increase in opening percentage and hence decrease in the surface on which load is applied. On the other hand, the rectangle shape of stiffener has a better performance due to higher moment of inertia and easier application compared to other shapes. By studying the joint effects of these factors, it can be suggested that developing opening and application of an appropriate stiffener can significantly reduce the amount of plate displacement compared to other types.

Application of box columns in steel moment frames is very common due to its bidirectional flexural resistance and also its shape which provides suitable surfaces for connection of beams in both directions. In Iran, because of limited availability of rectangular HSS sections, typically built-up box columns are applied which are fabricated by welding four steel plates to each other. According to seismic provisions, within a zone adjacent to the connection point of beam to column, flange and web plates of built-up box columns shall be joined by CJP groove welds. Because of the cost and difficulty of groove welding and concerns about achieving full penetration of weld in box sections, besides the common practice for fabrication of box sections in Iran by means of fillet-welded corner-outside joints, in this research seismic performance of moment connections between I-Shape beams and built-up box columns with corner welded joints was investigated experimentally. For this purpose, two specimens representative of special moment frames and two specimens representative of intermediate moment frames, all fabricated by built-up box columns using fillet welds or CJP groove welds, were designed and investigated. Investigation of the seismic performance of the specimens has been performed thru applying the cyclic load pattern presented in AISC341-16 standard. The results showed the capability of all 4 samples to satisfy the requirements for the required drift angle according to the specified load pattern.

The aim of this research is to study the parameters of nonlinear dynamic behavior of steel tall buildings having a compound braced-tube resistant skeleton with belted trusses in higher levels. For this purpose, four 30-story study models have been designed in 3D. The first study model has a resistant skeleton without a belted truss. Yet, the remaining three structural models, each have a belted truss in higher levels with layouts of one, two and three stories, respectively. Numerical study results of this research are acquired according to a set of time-history nonlinear analyses on the mentioned study models. The chosen ensemble of three-component ground motions includes six highly powerful near-field records and one far-field record. Assessing study results reveal that applying belted trusses in tall braced-tube skeletons would lead in a remarkable increase in stiffness and a growth in the capability to absorb the earthquake’s kinetic energy. This issue also results in a large decrease in lateral displacement and dynamic drift of the structure and will therefore cause an increase in using the axial capacity of peripheral columns of the structure plan. Thus it becomes possible to introduce the application of resistant structures with belted trusses in structural skeletons of high-rise buildings, especially in areas with high seismicity as a suitable and efficient alternative plan compared to other structural systems.

The studies have shown that the site characteristics such as soil layers properties and layer thickness can effect on the ground input motion and might change the acceleration frequency content and seismic duration. This research aims to study the effects of site characteristics on the ground response, and the response of the constructed buildings. In order to study the site effects on the ground seismic response, 14 far and near fault earthquake were considered and linear and nonlinear analysis on four different sites was performed. Additionally, one to four story buildings were modeled and the responses were analyzed using SAP 2000 software. Generally, the ground response related to the far and near fault earthquakes, the seismic input motion is amplified while passing through the earth layers and considering the acceleration, the maximum seismic motion increases. The smaller the maximum input acceleration of the seismic input of far fault earthquake, the less is the nonlinear and linear responses. For the cases with the larger near fault earthquake maximum ground acceleration, the analysis of the response, the response analysis using the linear equivalent approach shows that the soil layer of the input motion is amplified while passing through the soil layers. Comparing the graphs of the maximum acceleration versus the depth for the far fault earthquake, it can be inferred that the procedure cannot be generalized for the entire results of the far fault earthquakes. The maximum displacement in the depth increased with increasing the soil deposits thickness. For the similar stories buildings overlaid on the soil deposits, in both shallow and deep cases, the maximum displacement decreases with depth. On the other hand, the maximum obtained displacement in the linear and nonlinear times history analysis increases while increasing the number of building stories.

In this paper flexural buckling load for tapered columns has been evaluated (in-plane buckling of frame). The studied issue is about two-bay frames. Their three bases are hinged, and sway is permitted. The analysis is based on the answer of the deformation differential equation of the column, imposing the boundary conditions at the tips of the columns, and the displacement compatibility equations at the nodes of the members. Therefore, a set of equations could be obtained. When the corresponding square matrix of the equations collection is available, the critical load will be calculated. The critical load is the minimum root of the characteristic equation. This equation is obtained by equating the determinate of that matrix to zero. The results of the analysis are compared with the other methods of other researchers in some examples. The comparison showed that the introduced method can calculate the critical load with a good accuracy. This method can be generalized for other frames made of tapered members.

The strength and deformation capacities of the structural elements are affected by the cumulative damage of that component. For this purpose the loading protocols used for investigating the performance of the connections should give an accurate estimation of the structural components capacities and yield appropriate simulation of the reality. It is essential to investigate the differences and features of the loading protocols. On the other hand, regarding the widespread use of the moment connections of I-shaped beam sections in the box-section columns, investigating the seismic performance of these moment connections is of vital importance. Meanwhile, the majority of code details for accepting moment connections are presented for H-shaped columns. For this purpose 12 types of RBS and WUF-W moment connections with box-section columns were designed and examined as analytical models in the study. The seismic behavior and difference in performance of these two types of moment connections were investigated and compared at the level of the relative displacement acceptance in the codes and also the collapse threshold under SAC and ATC-24 loading protocols. In continuation, while investigating the demand and applied energy, and the features and differences between the loading protocols, the conditions for strength loss at the collapse threshold of moment connections in the special moment resisting frame are also proposed.